In 2014, the IMWG has added SLiM criteria (bone marrow plasmacytosis ≥ 60%, FLC i/u ≥100 along with the iFLC ≥ 100 mg/L, > 1 focal lesion on MRI) to the CRAB criteria (calcium elevation, renal insufficiency, anemia), as Myeloma Defining Events.
The iFLCr threshold (100) was defined because it was the cut-off associated with a 79% risk of progression to MM (Multiple Myeloma) or AL (AL amyloidosis) within 24 months, and with a specificity of 97% (Larsen JT et al, Leukemia, 2013).
In addition to this 100 ratio, the IMWG has then introduced the 20-20-20 system for assessing the Smoldering Multiple Myeloma (SMM) to MM progression. In that system, a patient with SMM receives 1 risk point for each of the following (M-spike>20 g/L, iFLCr>20 and BMPC>20%). This score is notably used for trial stratification and eligibility.
This publication indicates that the FLC cut-points can be used with Sebia ELISA FLC tests and allow for comparability within the field, to ensure an appropriate patient management.